1. Field of the Invention
This invention relates to detecting tampering of a device and more particularly relates to tamper evident devices for protecting fiscal printers and other electronic devices.
2. Description of the Related Art
In most countries, sellers of goods and services are required to collect taxes, such as sales taxes, which are later collected by governmental tax agencies. Point of Sale (“POS”) systems are typically used to record transaction data using transaction recording devices. For example, a fiscal printer may be provided with the POS system to record and print sales receipts showing an amount of taxes that have been collected by a particular merchant. These records and receipts may then be used by the government tax agencies to audit merchants and ensure that the amount of taxes collected by a merchant equals the amount of taxes that are passed from the merchant to the government.
In order to ensure integrity of the tax data recorded by a fiscal printer, it is important that the data be protected from tampering. A conventional fiscal printer typically uses an existing single or double station printer platform and adds logic devices in an enclosure at the bottom of the fiscal printer in order to comply with governmental regulations. The enclosed logic devices may include devices such as an electronic journal and fiscal memory which are used to electronically store recorded tax data. Such logic devices are typically enclosed in a drawer or compartment that slides into the printer beneath the existing printer platform so as to be protected from tampering.
Some countries have specific tamper-proof requirements for fiscal printers and other transaction recording devices. Thus, conventional fiscal printers in most countries include several tamper-proof measures. For example, a screw or screws for accessing the inside of the printer may be physically sealed or the fiscal memory and electronic journal may be imbedded in epoxy to prevent access to those devices. However, such tamper proofing measures have proven insufficient, because the only way for an auditor to know if a device has been tampered with is by visual inspection of the device.
Some conventional systems, have utilized a capacitor-based tamper switch to electronically detect when a tamper occurs, but such switches have also proved insufficient. This is because a capacitor provides only a single bit of information, so it can be easily bypassed or can result in frequent false tampers being recorded. Thus, tampering remains a problem in most conventional fiscal printing systems.